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Photosynthesis
Converts solar energy into the chemical energy of a carbohydrate in
this way:
Solar energy + carbon dioxide + water → carbohydrate + oxygen
Photosynthetic organisms include plants, algae, and certain bacteria.
These organisms are called producers; they synthesize organic
molecules from raw materials.
Photosynthetic Organisms
Nearly all life is dependent on solar energy because:
1)
Photosynthetic organisms use solar energy to produce
organic nutrients.
2) Almost all organisms depend either directly or indirectly
on these organic nutrients to sustain themselves.
3)
Photosynthetic organisms provide food for other
organisms, known as consumers.
4) The bodies of plants became the coal or other fossil fuels
used today.
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Structure and Function of Chloroplasts
Chloroplasts are the organelles that carry on
photosynthesis.
Mesophyll cells in the middle of a leaf house chloroplasts
Mesophyll cells are protected from drying out by a waxy
cuticle.
Pores called stomata allow CO2 and O2 to enter the leaf.
Visible Light
• Radiant energy from the sun (solar energy) can be described in
terms of its wavelength and its energy content.
• The colors in visible light range from violet (the shortest
wavelength and highest energy) to blue, green, yellow, orange,
and red (the longest wavelength and lowest energy).
Visible Light & Plants
• Pigments (chlorophylls and carotenoids) found within
photosynthesizing cells, are capable of absorbing various portions of
visible light.
• Both chlorophyll a and chlorophyll b absorb violet, blue, and red light
best.
• Leaves appear green because green light is reflected and only
minimally absorbed.
Photosynthetic Reactions
•It is an oxidation-reduction reaction, or redox reaction for short.
•Oxidation is the loss of electrons; hydrogen atoms are removed from glucose.
•Reduction is the gain of electrons; oxygen atoms gain electrons.
•Remember OIL RIG (oxidation is loss, reduction is gain)
Overview of Photosynthesis
• A simplified overall equation for photosynthesis is:
• Solar energy + 6CO2 + 6H2O → C6H12O6 + 6O2
• During photosynthesis, water molecules are oxidized; they
lose electrons (e-) along with hydrogen ions (H+).
• Also, CO2 is reduced and gains electrons given up by H2O.
• Electrons from H2O are energized by the sun.
Two Sets of Reactions
• Photosynthesis is divided into two sets of reactions, as
implied by the term “photosynthesis”:
• “Photo” refers to the light-dependent (needs light)
reactions that capture energy from the sun
• Photosystem II
• Photosystem I
• “Synthesis” refers to the light-independent (does not need
light) reactions that produce carbohydrate.
• Calvin Cycle
Light-Dependent Reactions
• During the light-dependent reactions, light energy is absorbed by
chlorophyll molecules. ATP and NADPH is produced.
• Inside the chloroplast, water is split to produce oxygen, hydrogen ions,
and electrons, the starting ingredients for photosynthesis
Photosystem II
• The electrons are excited by incoming light energy (from the sun).
These excited electrons are passed through a series of electron carriers.
Energy from these excited electrons is used to pump hydrogen ions
through the chloroplast
• An enzyme (ATP Synthase) uses the energy from these moving ions to
generate ATP.
Light-Dependent Reactions
Photosystem I
• Electrons are excited by incoming light energy (from the sun). These
excited electrons are passed through a series of different electron
carriers (called Photosystem I).
• As electrons pass down this chain, they combine with the molecule
NADP+ to form NADPH
Electron Transport System
Light-Independent Reactions
• The light-independent reactions do not need light and
consist of the Calvin cycle.
• During the Calvin Cycle, Carbon Dioxide (CO2) is taken
up by the plant (from the atmosphere)
• During the Calvin cycle, ATP and NADPH (made from the
light dependant reactions) add phosphates and electrons to
CO2, and convert it to glyceraldehyde 3- phosphate, or
G3P
• G3P is a type of sugar which a plant can easily convert to
glucose. This glucose can then be used as a source of
stored energy for the plant
The Calvin Cycle
Overview of Photosynthesis